I think you will want separate your command out into 3 lines.
wait
"{pathname of system folder}\msiexec.exe" /p
"__Download\Ac705RdP_efgj.msp" REINSTALLMODE=omus REINSTALL=all REBOOT=REALLYSUPPRESS /qb! wait
"{pathname of system folder}\msiexec.exe" /p
"__Download\Rdr707.msp" REINSTALLMODE=omus REINSTALL=all REBOOT=REALLYSUPPRESS /qb! wait
"{pathname of system folder}\msiexec.exe" /p
"__Download\Rdr708.msp" REINSTALLMODE=omus REINSTALL=all REBOOT=REALLYSUPPRESS /qb!
Also keep in mind that an MSP is keyed to a specific Product ID (PID). If the MSI that you are trying to patch is not present on the system, then msiexec is going to throw an error to that effect.
Is this a per-machine or per-user MSI install? Per-user installs can further complicate things.
Using the code you quoted above (using C:) does work. It does appear that the executable is running as a per-user MSI install.
Thanks
Updated
Looks like the knowledgebase article has changed so you’ll have to take my word for it. I’ll see if I can find it somewhere else. You can try the command and it does work though.